Galleries

Metals Chronic Concentration-Response Gallery

The Metals Chronic Concentration-Response Gallery is a gallery
of plots and source data describing the responses of aquatic
organisms to chronic exposures to metals, including
arsenic, cadmium, chromium, copper, lead, mercury,
nickel, selenium and zinc.
These
data are particularly valuable because they include longer
term exposures, multiple life stages and sublethal as well as
lethal effects. Results are presented as fitted functions and
concentrations resulting in prescribed proportions affected
(EC5, EC10, EC20 and EC50). Confidence intervals may be
found in the Model Parameters and Benchmarks worksheets.

What are the source data for these plots?

The data used for these plots
were extracted from toxicity test results originally published
between 1968 and 1996. The tests selected were judged to be
suitable for deriving national ambient water quality criteria
by the database developers, David Hansen and Glenn Thursby of
the U.S. EPA National Health and Environmental Effects
Research Laboratory in Narragansett, RI. The version of the
data base used here was quality assured, edited, and published
in U.S. EPA (2005). The References tab of this module
lists that report and the statistical methods paper (Kerr and Meador 1996).

How were plots generated?

Plots were successfully modeled for 38 of the 120 datasets
using the method described by Kerr and Meador (1996).
Confidence intervals were
calculated for both the exposure concentration (red dashed
lines, Figure 1) and the proportion responding (blue dashed
lines, Figure 1). Some
papers reported only mean responses without standard
deviations or results for replicates. For these sets,
surrogate standard deviations were derived based on the
expected variance for that type of response (see U.S. EPA
2005). Linear interpolation was also used to estimate the EC5, EC10, EC20 and EC50
benchmark values for those datasets exhibiting both a
concentration-response relationship and sufficient data points
(Figure 1, right). See U.S. EPA (2005) for more detail on
the methods.